The leukotrienes are a group of biologically active mediators derived from arachidonic acid through the action of lipoxygenase enzyme systems. The leukotrienes are potent smooth muscle contracting agents, particularly on respiratory smooth muscle, but also on other tissues as well. In addition, they promote mucous production, modulate vascular permeability changes and are potent inflammatory mediators in human skin. There are two groups of leukotrienes derived from the common unstable precursor Leukotriene A.sub.4. The first of these are the peptido-lipid leukotrienes, the most important being Leukotrienes C.sub.4 and D.sub.4. These compounds collectively account for the biologically active material known as the slow reacting substance of anaphylaxis ("SRS-A").
The most important compound in the second group of leukotrienes, namely dihydroxy fatty acids, is Leukotriene B.sub.4. This compound is a potent chemotactic agent for neutrophils and eosinophils and, in addition, may modulate a number of other functions of these cells. It also affects other cell types such as lymphocytes and, for example, may modulate the action of suppressor cells and natural killer cells. When injected in vivo, in addition to promoting the accumulation of leukocytes, Leukotriene B.sub.4 is also a potent hyperalgesic agent and can modulate vascular permeability changes through a neutrophil dependent mechanism. Both groups of leukotrienes are formed following oxygenation of arachidonic acid through the action of a lipoxygenase enzyme. See, for example, D. M. Bailey et al., Ann. Rpts. Med. Chem., 17, 203 (1982).